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10 results for “carbon isotopic fractionation”
Acid fractionation during carbonate digestion with phosphoric acid – Assessment of two different techniques applied for clumped and stable isotope analysis using a Tuneable Infrared Laser Differential Absorption Spectrometer (TILDAS) [dataset]
<p>Date files : </p> <table> <tbody> <tr> <td> <p>Data 1 (Relationship between Mixing ratio difference of sample and WRG and D638 value).xlsx;Data 2 (Role of bulk isotope composition (δ628 & δ636) on Δ638).xlsx;Data 3 (CDES scale conversion).xlsx;Data 4 (VPDB scale conversion for d628 and d636).xlsx;Data 5 (Reference material values).xlsx;Data 6 (Break seal method acid fractionation factor of calcite).xlsx;Data 7 (IAB method acid fractionation factor of calcite).xlsx</p> </td> </tr> </tbody> </table>
Contents and isotope carbon compositions (δ13C) of main biochemical fractions in organs at different growth stages in Phyllostachys edulis
<p><em><span>Phyllostachys edulis</span></em><span> is a spectacularly fast-growing species that completes its height growth within </span><span>two</span><span> months after the shoot emerges </span><span>without producing leaves</span><span> (fast-growing period, FGP). This phase was considered heterotrophic, the carbon necessary for the growth being transferred from the mature culms via the rhizomes, although previous studies observed key enzymes and anatomical features related to C<sub>4</sub>-carbon fixation in developing culms. </span><span>We tested whether C<sub>4</sub>-photosynthesis or dark-CO2 fixation through anaplerotic reactions significantly contributes to the FGP, resulting in differences in the natural abundance of </span><span>δ<sup>13</sup>C</span><span> in bulk organic matter and organic compounds. Further, pulse-<sup>13</sup>CO<sub>2</sub>-labelling was performed on developing culms, either from the surface or from the internal hollow, to ascertain whether significant CO<sub>2</sub> fixation occurs in developing culms.</span><span> δ<sup>13</sup>C of</span><span> young </span><span>shoots and developing culms were higher (-26.3–-26.9‰) </span><span>compared to all organs of mature bamboos (-28.4</span><span>–</span><span>-30.1</span><span>‰). </span>Developing culms contained chlorophylls, most observed in the skin tissues. After <span>pulse-<sup>13</sup>CO<sub>2</sub>-labelling, t</span>he polar fraction extracted from the skin tissues was slightly enriched in <sup><span>13</span></sup><span>C, </span>and only a weak <sup><span>13</span></sup><span>C </span>enrichment was observed in inner tissues<span>. Main carbon source sustaining the FGP was not assimilated by the developing culm, while a </span><span>limited anaplerotic fixation of respired CO<sub>2</sub></span><span> cannot be excluded and is </span>more likely than <span>C<sub>4</sub>-</span>photosynthetic carbon fixation<span>.</span></p>
Contents and isotope carbon compositions (δ13C) of main biochemical fractions in organs at different growth stages in Phyllostachys edulis
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Carbon and hydrogen isotope fractionation during uncultured aerobic oxidation of short-chain alkanes that discharged from a natural hydrothermal system
<p>Aerobic oxidation of short-chain alkanes was observed in gas samples from the Lutao intertidal hydrothermal vents in Taiwan, during storage without adding strains and replenishing substrates at 20 <sup>o</sup>C up to 29 months. The carbon isotope fractionation factors (<em>ε<sub>C</sub></em>) of methane (C<sub>1</sub>), ethane (C<sub>2</sub>), and propane (C<sub>3</sub>), were calculated using the Rayleigh fractionation equation to be -37.1 ± 7.5‰, -14.8 ± 4.8‰, and -4.7 ± 5.2‰, respectively. The hydrogen isotope fractionation factor (<em>ε<sub>H</sub></em>) of methane was determined to be -281 ± 187‰. DNA sequencing of the 16sRNA gene in the vent fluids suggests that aerobic oxidation is dominated by methanotrophs of the genera <em>Methylomicrobium</em> and <em>Methylophaga,</em> which use the ribulose monophosphate pathway (RuMP). The degrees of isotope fractionation (<em>ε<sub>C</sub></em> and <em>ε<sub>H</sub></em> values) herein are larger than previously reported values, possibly due to the limited O<sub>2</sub> supply and low abundance of aerobic methane-oxidizing bacteria in the experiments. Since the fractionation factor of methane is higher than those of ethane and propane, the aerobic oxidation of thermogenic or microbial alkanes could produce carbon isotope reversal, which is frequently noted as a trait of abiotic hydrocarbons. This work demonstrates that in addition to anaerobic microbial oxidation, aerobic oxidation with a low cell density can also produce significant isotope fractionation of alkanes in geological closed/semi-closed environments that are characterized by moderate temperatures and a limited supply of substrates and O<sub>2</sub>; these environments include cold seeps, mud volcanoes, and low-temperature hydrothermal aquifers/reservoirs.</p>
Alkenone carbon isotopic fractionation and sea surface temperature trends from 30 to 16 Ma. Sites IODP 1406, ODP 1168 and ODP 925
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Physiological control on carbon isotope fractionation in marine phytoplankton
<p><span>One of the great challenges in biogeochemical research over the past half a century has been to quantify and understand the mechanisms underlying stable carbon isotope fractionation (εp) in phytoplankton in response to changing CO2 concentrations. Partly, this interest is grounded in the use of fossil photosynthetic organism remains as a proxy for past atmospheric CO2 levels. Phytoplankton organic carbon is depleted in 13C compared to its source because of kinetic fractionation by the enzyme RubisCO during photosynthetic carbon fixation, as well as through physiological pathways upstream of RubisCO. Moreover, other factors such as nutrient limitation, variations in light regime as well as phytoplankton culturing systems and inorganic carbon manipulation approaches may confound the influence of aquatic CO2 concentration ([CO2]) on εp. Here, based on experimental data compiled from the literature, we assess which underlying physiological processes cause the observed differences in εp for various phytoplankton groups in response to C-demand/C-supply (i.e., POC production/[CO2]) and test potential confounding factors. Culturing approaches and methods of carbonate chemistry manipulation were found to best explain the differences in εp between studies, although daylength was an important predictor for εp in haptophytes. Extrapolating results from culturing experiments to natural environments and for proxy applications therefore requires caution, and it should be carefully considered whether culture methods and experimental conditions are representative of natural environments.</span></p>
Light calcium isotope anomaly observed in continental basaltic lavas: a mixed signal of recycled carbonate and fractionation during melting
<p>Table 1 and Supplementary Tables S1 to S7 which support for the manuscript 'Light calcium isotope anomaly observed in continental basaltic lavas: a mixed signal of recycled carbonate and fractionation during melting'.</p>
Physiological control on carbon isotope fractionation in marine phytoplankton
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LBA-ECO CD-06 Isotopic Composition of Carbon Fractions, Amazon Basin River Water
This data set includes measurements of standard geochemical variables, dissolved CO2, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), fine particulate organic carbon (FPOC), and coarse particulate organic carbon (CPOC) in samples taken from 60 Amazonian river locations across the Amazon Basin from 1991 to 2003 (Mayorga et al., 2005). The 14C and 13C isotopic composition of DIC was measured on samples collected between 1991 and 2003. The 14C composition of organic carbon fractions was measured on samples collected from 1995 through 1996. There are four comma-delimited data files with this data set. Note that site descriptions include a categorization of each site by topography according to the percentage of the drainage area above 1,000 m elevation (Mayorga et al., 2005). Only means of geochemical and carbon-fraction results are provided. Both individual 13C and 14C measurements and mean results are provided.
Supplementary Dataset for "Experimental Studies of Clumped Isotope Fractionation During Carbon Dioxide Hydration"
<p>This supplementary dataset contains raw isotopic values used to generate figures in the article "Experimental Studies of Clumped Isotope Fractionation During Carbon Dioxide Hydration" by Guo et al. </p>
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